Development of ZnO buffer layers for as‐doped CdSeTe/CdTe solar cells with efficiency exceeding 20%

The front buffer layer plays an important role in CdSeTe/CdTe solar cells and helps achieve high conversion efficiencies. Incorporating ZnO buffer layers in the CdSeTe/CdTe device structure has led to highly efficient and stable solar cells. In this study, the optimization of ZnO buffer layers for CdSeTe/CdTe solar cells is reported. The ZnO films are radio frequency sputter‐deposited on SnO₂:F coated soda‐lime glass substrates. The substrate temperature for the ZnO deposition is varied from 22 to 500 °C. An efficiency of 20.74% is achieved using ZnO deposited at 100 °C. The ZnO thickness is varied between 40 nm and 75 nm. Following the ZnO depositions, devices were fabricated using First Solar's CdSeTe/CdTe absorber, CdCl₂ treatment, and back contact. The optimal ZnO deposition temperature and thickness is 100 °C and 65 nm, respectively. The STEM‐EDX analysis shows that within the detection limits, chlorine is not detected at the front interface of the devices using ZnO deposited at 22 °C and 100 °C. However, depositing ZnO at 500 °C results in chlorine segregation appearing at the ZnO/CdSeTe boundary. This suggests that chlorine is not needed to passivate the ZnO/CdSeTe interface during the lower temperature depositions. The nanocrystalline ZnO deposited at lower temperatures results in a high‐quality interface.